1. Field of the Invention
This invention relates to image-forming materials, specifically to dye-providing compounds which, in the presence of silver ions and/or a soluble silver complex, undergo a cleavage reaction to liberate a diffusible coupler dye.
2. Description of the Related Art
U.S. Pat. No. 3,719,489 discloses silver ion assisted cleavage reactions useful in photographic systems. As disclosed therein, photographically inert compounds are capable of undergoing cleavage in the presence of silver ions made available imagewise during processing of a silver halide emulsion to liberate a reagent, such as, a photographically active reagent or a dye in an imagewise distribution corresponding to that of said silver ions. In one embodiment disclosed therein, color images are produced by using as the photographically inert compounds, color-providing compounds which are substantially non-diffusible in the photographic processing composition but capable of undergoing cleavage in the presence of the imagewise distribution of silver ions and/or soluble silver complex made available in the undeveloped and partially developed areas of a silver halide emulsion as a function of development to liberate a more mobile and diffusible color-providing moiety in an imagewise distribution corresponding to the imagewise distribution of said ions and/or said complex. The subsequent formation of a color image is the result of the differential in diffusibility between the parent compound and liberated color-providing moiety whereby the imagewise distribution of the more diffusible color-providing moiety released in the undeveloped and partially developed areas is free to transfer.
Color-providing compounds useful in the above process form the subject matter of U.S. Pat. No. 4,098,783, a continuation in part of said U.S. Pat. No. 3,719,489. The color-providing compounds disclosed therein may comprise one or more dye radicals and one or more 1,3-sulfur-nitrogen moieties. For example, they may comprise one complete dye or dye intermediate and one cyclic 1,3-sulfur-nitrogen moiety. Alternatively, the color-providing compounds may comprise two or more cyclic moieties for each dye radical or dye intermediate and vice versa. Particularly useful dye-providing compounds disclosed therein comprise a dye containing from 1 to 4 and preferably 1 or 2 cyclic 1,3-sulfur-nitrogen groups and may be represented by the formula EQU D--[(L).sub.m--1 --Y].sub.n (A)
wherein D represents a dye radical, i.e., the radical of an organic dye possessing at least one carbon atom, L is a divalent organic linking group containing at least one carbon atom, m is a positive integer 1 or 2, n is a positive integer from 1 to 4, and Y is a cyclic 1,3-sulfur-nitrogen group. Indophenol, indoaniline, and azomethine dyes are broadly disclosed therein as useful dye radicals, although no specific examples are given.
European Patent No. 0 073 245 describes certain polymers, among others, which comprise recurring units containing cyclic 1,3-sulfur-nitrogen groups of the type disclosed in the aforementioned U.S. Pat. No. 4,098,783. These polymeric cyclic 1,3-sulfur-nitrogen compounds are capable of undergoing cleavage in the presence of an imagewise distribution of silver ions or a silver complex to release a photographically useful group, e.g., an image dye-providing material, corresponding to said imagewise distribution.
Japanese Kokai 59-180548 having a Laid-Open date of October 13, 1984 discloses a heat-developable silver halide photosensitive imaging system wherein the dye-providing material contains a heterocyclic ring containing a nitrogen atom and a sulfur or selenium atom which heterocyclic ring is subject to cleavage in the presence of silver ions to release a diffusible dye. An example of a suitable dye-providing material is a thiazolidine dye such as disclosed in the aforementioned U.S. Pat. No. 4,098,783. The process involves imagewise exposing the photosensitive system to light and subsequently or simultaneously heating the photosensitive system under a substantially water-free condition, in the presence of a base or base precursor, whereby an oxidation-reduction reaction between the exposed photosensitive silver halide and a reducing agent occurs. In the exposed areas a negative silver image is formed. In the unexposed areas, the silver ion, present in inverse proportion to the silver image, causes the heterocyclic ring of the dye-providing material to be cleaved releasing a diffusible dye. The diffusible dye is then transferred to an image-receiving layer whereby a positive dye image is formed.
Useful dye radicals to be used in the dye-providing materials for photographic and particularly for photothermographic applications, are coupler dyes, i.e., dyes formed by the oxidative coupling of a phenylene diamine with a color coupler, e.g., azomethine, indoaniline, indamine, and indophenol dyes, as disclosed in the copending U.S. patent application, Ser. No. 07/923,843 of M. Arnost et al filed Jul. 31, 1992. Coupler dyes are well-known dyes having desirable hues for color reproduction. However, modification of these known coupler dyes to incorporate cyclic 1,3-sulfur-nitrogen moieties can undesirably influence their color characteristics by shifting the absorption of the starting coupler dye.
It has now been found that by substituting the developer portion of known coupler dyes in a particular manner with aldehyde or ketone functionalities, those functionalities being necessary to prepare the cyclic 1,3-sulfur-nitrogen dye-providing compounds, the chromophores of the resulting aldehyde and ketone coupler dyes are virtually unchanged. In addition, the aldehyde and ketone substituted coupler dyes and the dye-providing compounds produced therefrom are readily synthesized.